The present invention is concerned with the operation of a refrigeration heat pump when heating of the conditioned space is being demanded.
The air supplied to the conditioned space from a heat pump is frequently at a temperature of 90.degree. to 100.degree. F., which is lower than most other heating systems. This is due to the heat pump having a lower temperature rise across the indoor heat exchanger as compared to a gas-fired furnace, for example. The heat pump rise may be on the order of 25.degree. F., whereas the gas-fired furnace may be on the order of 65.degree. F. Therefore, there is a potential for complaints about cold drafts, especially during the time period that the indoor heat exchanger coil is being heated to its steady state condition.
Typical operation of a conventional heat pump in the heating mode may be explained as follows. Upon a request for heating by a room thermostat, a refrigerant compressor would be energized. An indoor fan for circulating air over an indoor heat exchanger or coil would be energized at substantially the same time as the compressor is energized. The indoor fan in a conventional system may be energized by a relay that closes a contact to energize the indoor fan when the compressor is energized, for example. Therefore, in the conventional heat pump system, the indoor fan will operate when the compressor operates. This control method results in air being circulated through the indoor coil for some period of time before the coil has been heated to its steady state temperature. During this time period, the occupants of the space may be subjected to discharge temperatures below the steady state condition. This lower discharge air temperature may cause the occupants to experience cool drafts which are generally objectionable during the heating season.